A microcontroller with at least three ADs for the adjustment pots, one digital input for the switch, three digital outputs for the relay controls, plus the necessary transistors, diodes, resistors, and caps to decorate the whole assemblage. If an internal RC oscillator would be accurate enough, you'd not even need a crystal or clock for the thing.
Not a single 555, certainly. Could probably wizard-up something with multiple 555s but that seems unnecessarily painful, rather like walking up stairs on one's hands.
Also: I assume that if the switch is released before the initial time delay completes, the entire cycle is discarded and must begin anew. However what happens, for example, if the switch is released after relays 2 and 3 have shut but then the switch is closed again before relay 3 has opened?
Rly1 will energize immediately when the button is pressed, and will stay energized as long as it is depressed. When you release it, the relay will stay energized while C1 discharges. The pot (configured as a variable resistor) can be adjusted for the required off delay. That takes care of the on and off requirements for Rly1.
The same circuit can be used to set the drop out time for Rly3, with a smaller value for the cap, since the maximum drop out time is .5 seconds for that relay. The contacts of Rly2 replace the pushbutton in the diagram for the Rly3 circuit. That takes care of the on and off requirements for Rly3.
Rly2 must drop out when the button is released, so it is connected to the point marked A on the diagram. That takes care of the Rly2 off requirement.
The on requirement for Rly2 is different - there must be an adjustable delay from the time the button is pressed until the relay energizes. Here's the diagram:
| | that wont cause a problem its to improve control on a welder | relay 1 is gas relay 2 is main power on no 3 is wire feed | | I would most likely use a relay to start the circuit ie it would be | activated by the press switch | | thanks Andrew |
Reading this I think you'll need a professional PLC type of solution. It sure can be done by electronics and a micro but you'll need experience to complete a project like this without accidents.
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